1. Field of the Invention
The present invention relates to a marine propulsion device.
2. Description of the Related Art
In an outboard motor, it is possible for a phenomenon to occur in which an engine is driven in a reverse direction (referred to below as an “inversion phenomenon”) by the propeller being rotated in a reverse orientation to a drive direction due to a torque applied by a water current. The cause for the occurrence of such an inversion phenomenon is described below. First, a boat operator sets a shift state to a neutral position in order to decelerate during forward progression. However, when a boat continues forward progression due to inertia, the propeller rotates normally due to water current hitting against the propeller. Next, the boat operator sets the shift state to a reverse position in order to further decelerate. At this time, if a rotation torque of the propeller due to the water current is larger than the engine drive torque, the engine stops, and is then driven in the reverse direction. When the engine is driven in the reverse direction, water is drawn into an exhaust passage due to a pump action of a cylinder. In this case, when water infiltrates into the cylinder, there is a possibility that the engine is damaged. Alternatively, there is a possibility that a catalyst is damaged due to submersion of the catalyst in water in the exhaust passage.
In an outboard motor disclosed in Japanese Laid-open Patent Application Publication No. H4-266593, a one-way clutch is disposed between a drive shaft and a pinion gear. In the outboard motor disclosed in Japanese Laid-open Patent Application Publication No. 2004-276726, a vertical shaft is divided into a first shaft and a second shaft, and an electromagnetic clutch is disposed between the first shaft and the second shaft. Both of these apparatuses have a structure in which the one-way clutch is engaged during transmission of a motive force from the engine to the propeller shaft, and the one-way clutch is disengaged and a motive force is not transmitted from the propeller shaft to the engine.
In addition, in a marine propulsion apparatus disclosed in Japanese Laid-open Patent Application Publication No. 2000-280983, the drive shaft is divided into a drive-side portion and a driven-side portion and a buffer apparatus is disposed between the drive-side portion and the driven-side portion. In the outboard motor disclosed in Japanese Laid-open Patent Application Publication No. 2006-183694, the drive shaft is divided into an upper drive shaft and a lower drive shaft and a damper structure is disposed between the upper section drive shaft and the lower section drive shaft. Both of these apparatuses have a structure in which the drive shaft is divided into two members and in which transmission of a motive force from the propeller shaft to the engine is controlled using a buffer member which is disposed between the two drive shaft members.
In addition, in the marine propulsion apparatus disclosed in Japanese Laid-open Patent Application Publication No. 2008-274970, the inversion phenomenon is detected by detecting a rotation angle of the crank shaft. In a case in which the inversion phenomenon is detected, the marine propulsion apparatus prevents the infiltration of water into the engine by forcibly transferring the shift gear to the neutral state.